5.8 Overview of the Large Intestine, Rectum, and Anal Canal

Question 1

What are the Parts of the Large Intestine?

Answer 1

1. The Ileocaecal Valve (Sphincter)
2. The Caecum
3. The Appendix
4. The Ascending Colon
5. The Transverse Colon
6. The Descending Colon
7. The Sigmoid Colon

Question 2

What follows the Sigmoid Colon?

Answer 2

1. The Rectum

2. The Anal Canal

Question 3

What is the Ileocaecal Valve?

Answer 3

The Sphincter between the Ileum and the Caecum

Question 4

What is the Caecum?

Answer 4

A Blind Sac which leads into the Ascending Colon

Question 5

What is the Appendix?

Answer 5

An attachment to the Caecum, with no known function, but is a common site of infection (Appendicitis)

Question 6

What is the Ascending Colon?

Answer 6

1. The 1st Part of the Colon
2. It lies on the Right Side of the Abdomen, lateral to the Small Intestines
3. It is Retroperitoneal
4. It leads to the Transverse Colon

Question 7

What is the Transverse Colon?

Answer 7

1. The 2nd Part of the Colon
2. It lies Superiorly to the to the Small Intestines.
3. It is Intraperitoneal
4. It leads to the Descending Colon

Question 8

What is the Descending Colon?

Answer 8

1. The 3rd Part of the Colon
2. It lies on the Left Side of the Abdomen, lateral to the Small Intestines
3. It is Retroperitoneal
4. It leads to the Sigmoid Colon

Question 9

What is the Sigmoid Colon?

Answer 9

1. It is the Final Part of the Colon
2. It lies on the Left Side of the Abdomen, Infero-laterally to the Small Intestines
3. It is Intraperitoneal
4. It leads to the Rectum

Question 10

What is the Rectum?

Answer 10

1. It is a Straight Muscular Tube between the Sigmoid Colon and the Anal Canal
2. It has a Simple Columnar Epithelium (Mucosa)
3. It has a Thick Muscularis Externa

Question 11

What is the Anal Canal?

Answer 11

1. It is a short (2-3cm) Canal Between the Rectum and the Anus
2. It changes from a Proximal Simple Columnar Epithelium to a Distal Stratified Squamous Epithelium
3. It has a Thick Muscularis Externa ( internal anal sphincter- smooth muscles)
4. It has a Portion of Skeletal Muscle ( external anal sphincter- skeletal muscles)

the internal anal sphincter is smooth muscle, while the external anal sphincter muscle is skeletal muscle.

Question 12

What is the name of the Thick Muscularis Externa in the Anal Canal?

Answer 12

The Internal Anal Sphincter

Question 13

What is the name of the Skeletal Muscle in the Anal Canal?

Answer 13

The External Anal Sphincter

Question 14

What is the Mucosal Layer of the Colon formed of?

Answer 14

Simple Columnar Epithelium

Question 15

What is the Mucosal Layer of the Colon lined with?

Answer 15

Many Goblet Cells, in the Crypts

Question 16

What is the function of the Goblet Cells?

Answer 16

Produce mucous, to provide Lubrication for the movement of Faeces

Question 17

Is the Circular Muscle in the Muscularis Externa of the Colon ( except rectum, anal canal and anus) Complete?

Answer 17

Yes

Question 18

Is the Longitudinal Muscle in the Muscularis Externa of the Colon Complete?

Answer 18

No

Question 19

What makes the Longitudinal Muscle of the Colon?

Answer 19

Three Bands called Teniae Coli- incomplete muscle

Question 20

What is the Teniae Coli?

Answer 20

A Tendon-Like structure which runs the entire length of the Colon

Question 21

What do the Contractions of the Teniae Coli muscle produce?

Answer 21

Haustra

Question 22

What are Haustra?

Answer 22

is a contraction that gives the Colon its puckered appearance

Question 23

What is the main function of the Colon?

Answer 23

The Dehydration of the Chyme, as it forms Faeces

Question 24

How does water get absorbed from the Chyme?

Answer 24

1. Osmosis - through the alimentary lumen into the blood

2. Active transport of Sodium from the alimentary lumen into the blood

Question 25

What occurs due to the chyme residing for a long time in the Colon?

Answer 25

Bacterial Colonization

Question 26

What do bacteria in the Colon do?

Answer 26

Ferment Undigested Carbohydrates

Question 27

What is formed as a result of the Bacteria Fermenting Undigested Carbohydrates?

Answer 27

1. Short Chain Fatty Acids 2. Vitamin K 3. Gas (Flatus)

Question 28

What happens to the Short Chain Fatty Acids and Vitamin K. formed by the Bacteria?

Answer 28

It is reabsorbed back into the blood Vitamin K - cloting factor Short chain fatty acid - produce energy

Question 29

What happens to the Gas (Flatus) formed by the Bacteria?

Answer 29

It is expelled through the Anus

Question 30

What normally closes the Anus?

Answer 30

1. The Internal Anal Sphicter | 2. The External Anal Sphincter

Question 31

What is the Internal Anal Sphincter made of? And what controls it?

Answer 31

Smooth Muscle controlled by the Autonomic (Parasympathetic) Nervous System

Question 32

What is the External Anal Sphincter made of? And what controls it?

Answer 32

Skeletal Muscle controlled by Somatic Fibres

Question 33

What is the Physiology of defaecation?

Answer 33

1. An intense peritaltic wave of contraction (from the Colon to the Rectum) moves faecal matter into the Rectum 2. This causes distention of the Rectal Wall and activates mechanoreceptors in the rectum, cause the Defaecation reflex

Question 34

What nerves control the Defaecation Reflex?

Answer 34

Parasympathetic Nerves via the Pelvic Splanchnic Nerve

Question 35

What is the Defaecation Reflex?

Answer 35

1. Contraction of the Rectum 2. Relaxation of the Internal Anal Sphincter 3. Contraction of the External Anal Sphincter 4. An increase in Colon Peristalsis, increasing the pressure on the External Anal Sphincter 5. Relaxation of the External Anal Sphincter which will relax under voluntary control